EP3349376B1 - Appareil de génération de signal pam4 - Google Patents

Appareil de génération de signal pam4 Download PDF

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Publication number
EP3349376B1
EP3349376B1 EP17211038.9A EP17211038A EP3349376B1 EP 3349376 B1 EP3349376 B1 EP 3349376B1 EP 17211038 A EP17211038 A EP 17211038A EP 3349376 B1 EP3349376 B1 EP 3349376B1
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Prior art keywords
signal
optical
nrz
modulator
optical signal
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German (de)
English (en)
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EP3349376A1 (fr
Inventor
Hongmin Chen
Zhenwei Cui
Xi Huang
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HiSilicon Optoelectronics Co Ltd
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HiSilicon Optoelectronics Co Ltd
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    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04LTRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00Baseband systems
    • H04L25/38Synchronous or start-stop systems, e.g. for Baudot code
    • H04L25/40Transmitting circuits; Receiving circuits
    • H04L25/49Transmitting circuits; Receiving circuits using code conversion at the transmitter; using predistortion; using insertion of idle bits for obtaining a desired frequency spectrum; using three or more amplitude levels ; Baseband coding techniques specific to data transmission systems
    • H04L25/4917Transmitting circuits; Receiving circuits using code conversion at the transmitter; using predistortion; using insertion of idle bits for obtaining a desired frequency spectrum; using three or more amplitude levels ; Baseband coding techniques specific to data transmission systems using multilevel codes
    • HELECTRICITY
    • H03ELECTRONIC CIRCUITRY
    • H03KPULSE TECHNIQUE
    • H03K7/00Modulating pulses with a continuously-variable modulating signal
    • H03K7/02Amplitude modulation, i.e. PAM
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04BTRANSMISSION
    • H04B10/00Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/50Transmitters
    • H04B10/501Structural aspects
    • H04B10/503Laser transmitters
    • H04B10/505Laser transmitters using external modulation
    • H04B10/5053Laser transmitters using external modulation using a parallel, i.e. shunt, combination of modulators
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04BTRANSMISSION
    • H04B10/00Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/50Transmitters
    • H04B10/516Details of coding or modulation
    • H04B10/5161Combination of different modulation schemes
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04BTRANSMISSION
    • H04B10/00Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/50Transmitters
    • H04B10/516Details of coding or modulation
    • H04B10/54Intensity modulation
    • H04B10/541Digital intensity or amplitude modulation
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04LTRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00Arrangements for detecting or preventing errors in the information received
    • H04L1/0001Systems modifying transmission characteristics according to link quality, e.g. power backoff
    • H04L1/0002Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the transmission rate
    • H04L1/0003Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the transmission rate by switching between different modulation schemes
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04LTRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00Arrangements for detecting or preventing errors in the information received
    • H04L1/004Arrangements for detecting or preventing errors in the information received by using forward error control
    • H04L1/0056Systems characterized by the type of code used
    • H04L1/0061Error detection codes
    • H04L1/0063Single parity check
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04LTRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00Modulated-carrier systems
    • H04L27/0008Modulated-carrier systems arrangements for allowing a transmitter or receiver to use more than one type of modulation

Definitions

  • the present invention relates to the field of optical communications technologies, and in particular, to a PAM4 signal generation apparatus.
  • PAM4 pulse amplitude modulation
  • the PAM4 code includes four levels, and a quantity of levels of the PAM4 code is doubled relative to that of an NRZ signal. Therefore, a requirement on device linearity is increased. In an actual application, the four levels need to be evenly distributed to achieve optimal judgment. Therefore, a requirement on device linearity is relatively high. In addition, a baud rate of a PAM4 signal is decreased by a half relative to that of a binary on-off keying (OOK) signal in a case of a same bit rate, thereby reducing a requirement on a bandwidth of a device. Relative to a coherent system, the PAM4 code does not need a complex coding/decoding algorithm or a decorrelation algorithm, bringing remarkable advantages in power consumption and costs.
  • OOK binary on-off keying
  • Document US 2014/133870 A1 shows a method and an optical transmitter for generating multi-level optical signals, e.g. with 4 levels.
  • a first and second binary electrical signal is input to a first and second optical intensity modulator respectively.
  • An optical power splitter with ratio 2:1 is connected to another input of the first and second modulator.
  • An optical power combiner with ratio 1:1 is connected to the output of the first and second modulator.
  • an optical splitter with ratio 1:1 is used and an optical attenuator is connected between the second modulator and a combiner.
  • Document US 2009/279576 A1 shows an optical circuit.
  • a DFB laser supplies CW light to a first modulator and a second modulator.
  • a first data stream is supplied to first driver circuit which drives the first modulator.
  • the first modulator outputs a modulated optical data signal to a first output.
  • a second data stream is supplied to second driver circuit which drives the second modulator.
  • the second modulator outputs a modulated optical data signal to a second output.
  • the power from each output of the DFB laser is managed by a variable optical attenuator.
  • a PAM4 signal generation method based on an electro-absorption modulated laser EML
  • EML electro-absorption modulated laser
  • TOSA transmitter optical subassembly
  • a current mainstream technology is to generate a PAM4 signal based on an EML, for example, a 25 GHz EML is used to generate a PAM4 signal with 26.56 Gbauds.
  • the PAM4 raises a relatively high linearity requirement for a system. Therefore, a device of higher linearity generally obtains a PAM4 signal of higher quality.
  • a cut-off area is formed in an area of a relatively low voltage, and an absorption coefficient of an electro-absorption (EA) modulator of the EML no longer changes with a reduction in a voltage.
  • a saturation area is formed in an area of a relatively high voltage, and similarly, an absorption coefficient of the EA modulator no longer changes with an increase in a voltage.
  • This characteristic of the EML is quite conducive to an NRZ signal modulation code, may inhibit a level 0 and a level 1 of an NRZ signal, and is conducive to improving NRZ signal quality.
  • a PAM4 signal generation method based on a directly modulated laser (DML) Linearity of the DML is superior to that of an EML, but this does not mean that a PAM4 signal generated based on the DML is of quite good performance because the DML-based PAM4 signal has a performance loss in another aspect.
  • DML directly modulated laser
  • a difference between characteristics of high and low temperatures Because there is no temperature control unit in the DML, the characteristics of the high and low temperatures are deteriorated quite severely. In a case of a high temperature, not only a bandwidth of the device is quickly degraded, but also linearity is degraded, exerting relatively great impact on performance.
  • a bandwidth of the DML device is still a bottleneck in an engineering application.
  • a chirp effect Because the DML directly adjusts a current, a chirp effect may be accompanied in a signal modulation process. This is detrimental to a long-distance application scenario. In addition, the chirp effect of the laser and a chromatic dispersion effect of an optical fiber interact with each other, causing relatively high chromatic dispersion. 3. Currently, it is relatively difficult to design a high-linearity driver for the DML. Therefore, a high-quality PAM4 signal cannot be generated based on the DML.
  • the single-ended EML cannot generate a PAM4 signal of relatively high quality due to a linearity limitation
  • the single-ended DML cannot generate a PAM4 signal of relatively high quality either due to impact of the characteristics of the high and low temperatures and a noise characteristic that are of the single-ended DML device.
  • Embodiments of the present invention provide a PAM4 signal generation apparatus, to generate a high-quality PAM4 signal.
  • the embodiments of the present invention provide the following technical solutions.
  • An embodiment of the present invention provides a PAM4 signal generation apparatus, where the PAM4 signal generation apparatus includes a distributed feedback laser (DFB), a first electro-absorption (EA) modulator, a second EA modulator, a semiconductor optical amplifier (SOA), a polarization beam splitting rotator (PSR), a first electrical-signal generator, a first amplitude-limiting amplifier, a second electrical-signal generator, a second amplitude-limiting amplifier, a first direct-current power source, and a second direct-current power source; an input port of the DFB is connected to the first direct-current power source, and the DFB is connected to both the first EA modulator and the SOA by using two output ports; the first EA modulator is connected to both the first amplitude-limiting amplifier and the DFB by using two input ports, and an output port of the first EA modulator is connected to the PSR; the SOA is connected to both the DFB and the second direct-current power source by using two input ports, and an output port of
  • the PAM4 signal generation apparatus includes the DFB, the two EA modulators, the SOA, the PSR, the direct-current power sources, the two electrical-signal generators, and the two amplitude-limiting amplifiers.
  • the two electrical-signal generators and the two amplitude-limiting amplifiers are used to generate the two NRZ electrical signals
  • the DFB outputs the two optical signals
  • the SOA amplifies an optical power of one of the optical signals
  • the two EA modulators may generate the two NRZ optical signals by separately using the NRZ electrical signals and the optical signals including "a large signal and a small signal”
  • the two NRZ optical signals are multiplexed by the PSR to generate a PAM4 electrical signal.
  • a linearity requirement is greatly lowered.
  • the DFB, the two EA modulators, and the SOA are used, implementing a high-linearity PAM4 code.
  • PAM4 modulation is performed in an optical domain, and this prevents a PAM4 signal from being generated on an electrical signal.
  • an amplitude-limiting device may continue to be used, with no need to use an expensive linear electrical device, to modulate the electrical signal to the optical domain in a distortionless way. Therefore, a high-quality PAM4 signal can be generated in this embodiment of the present invention.
  • the first electrical-signal generator is configured to pre-compensate the first NRZ electrical signal according to a relative delay that is between the first NRZ electrical signal and the second NRZ electrical signal and that is on a transmission optical path.
  • a transmission time delay occurs, on a transmission optical path, on the two NRZ optical signals generated by the first EA modulator and the second EA modulator, that is, a skew is generated between the two NRZ optical signals
  • the skew between the two NRZ optical signals may be pre-compensated on the NRZ electrical signals. Therefore, an optical path compensation unit is not required on the optical path; in this case, a device design is further simplified, and optical path compensation does not need to be performed dedicatedly.
  • the second electrical-signal generator is configured to pre-compensate the second NRZ electrical signal according to a relative delay that is between the second NRZ electrical signal and the first NRZ electrical signal and that is on a transmission optical path.
  • a transmission time delay occurs, on a transmission optical path, on the two NRZ optical signals generated by the first EA modulator and the second EA modulator, that is, a skew is generated between the two NRZ optical signals
  • the skew between the two NRZ optical signals may be pre-compensated on the NRZ electrical signals. Therefore, an optical path compensation unit is not required on the optical path; in this case, a device design is further simplified, and optical path compensation does not need to be performed dedicatedly.
  • a current value of the first direct-current bias signal is less than a current value of the second direct-current bias signal.
  • direct-current bias signals required by the DFB and the SOA are different.
  • the first direct-current bias signal is set as required by the DFB during optical signal generation, and the second direct-current bias signal is set as required by the SOA.
  • a bias current value required by the DFB during work is less than a bias current value required by the SOA during work.
  • an optical power of the first optical signal is equal to the optical power of the second optical signal.
  • the DFB may generate two optical signals, which are the first optical signal and the second optical signal respectively. Because the two optical signals are output by a same DFB, the two optical signals have an exactly same wavelength, and the optical powers of the two optical signals may also be exactly the same.
  • the SOA is specifically configured to amplify the optical power of the second optical signal according to an optical power of the first optical signal to obtain the second optical signal that is after optical power amplification, where an optical power of the second optical signal that is after optical power amplification is twice the optical power of the first optical signal. If the optical power of the first optical signal is equal to the optical power of the second optical signal, the SOA amplifies the optical power of the second optical signal doubly, to obtain the second optical signal that is after optical power amplification. The optical power of the second optical signal that is after optical power amplification is twice the optical power of the first optical signal.
  • the first optical signal and the second optical signal are modulated by the first EA modulator and the second EA modulator respectively, and an optical power of the second NRZ optical signal is twice an optical power of the first NRZ optical signal, so as to meet a signal amplitude requirement of the PAM4 signal.
  • the optical power of the second NRZ optical signal generated by the second EA modulator is twice the optical power of the first NRZ optical signal generated by the first EA modulator.
  • the optical power of the second optical signal that is after optical power amplification is twice the optical power of the first optical signal.
  • the first optical signal and the second optical signal are modulated by the first EA modulator and the second EA modulator respectively, and the optical power of the second NRZ optical signal is twice the optical power of the first NRZ optical signal, so as to meet the signal amplitude requirement of the PAM4 signal.
  • the DFB is specifically configured to: adjust a reflection coefficient of a first end surface, adjust a reflection coefficient of a second end surface, generate the first optical signal by using the first end surface, and generate the second optical signal by using the second end surface.
  • the DFB needs to adjust both the reflection coefficient of the first end surface and the reflection coefficient of the second end surface when generating the two optical signals.
  • the reflection coefficient of the two end surfaces of the DFB are adjusted to make output optical powers of the two output ports be the same.
  • the first electrical-signal generator is specifically a first digital signal processor DSP; and the second electrical-signal generator is specifically a second DSP.
  • the DSPs may be used to generate the NRZ electrical signals.
  • a DSP may be selected according to an actual scenario to generate an NRZ electrical signal.
  • the DFB is specifically configured to: transmit the first optical signal to the first EA modulator by using a first passive optical waveguide, and transmit the second optical signal to the SOA by using a second passive optical waveguide.
  • the DFB is configured to: generate two optical signals from a same source, use the passive optical waveguides to separate the two optical signals, guide the two optical signals into the first EA modulator and the SOA respectively, and output the modulated optical signals from the two ports of the DFB respectively.
  • the embodiments of the present invention provide a PAM4 signal generation apparatus, to generate a high-quality PAM4 signal.
  • the terms “first”, “second”, and so on are intended to distinguish between similar objects, but do not necessarily indicate a specific order or sequence. It should be understood that the terms used in such a way are interchangeable in proper circumstances, which is merely a discrimination manner that is used when objects having a same attribute are described in the embodiments of the present invention.
  • the terms “include”, “contain” and any other variants mean to cover the non-exclusive inclusion, so that a process, method, system, product, or device that includes a series of units is not necessarily limited to those units, but may include other units not expressly listed or inherent to such a process, method, system, product, or device.
  • the PAM4 signal generation apparatus can generate a PAM4 optical signal in an optical domain.
  • Table 1 a principle of generating a PAM4 signal by using two NRZ signals is listed.
  • Table 1 Corresponding combinations for generating a PAM4 signal NRZ1 (least significant bit) NRZ2 (most significant bit) PAM4 0 0 0 1 0 1 0 1 2 1 1 3
  • a Gray encoding manner may also be used to implement mapping from an NRZ signal to a PAM4 signal in this embodiment of the present invention. For example, when the least-significant-bit NRZ signal is 0, and the most-significant-bit NRZ signal is 0, a generated PAM4 signal is 0; when the least-significant-bit NRZ signall is 1, and the most-significant-bit NRZ signal is 0, a generated PAM4 signal is 1; when the least-significant-bit NRZ signal is 0, and the most-significant-bit NRZ signal is 1, a generated PAM4 signal is 2; when the least-significant-bit NRZ signal is 1, and the most-significant-bit NRZ signal is 1, a generated PAM4 signal is 3.
  • a high-quality PAM4 signal may be generated after a single-ended EML is improved into a two-ended EML.
  • a PAM4 signal generation apparatus 100 provided in an embodiment of the present invention includes a distributed feedback laser (DFB) 101, a first electro-absorption (EA) modulator 102, a second EA modulator 103, a semiconductor optical amplifier (SOA) 104, a polarization beam splitting rotator (PSR) 105, a first electrical-signal generator 106, a first amplitude-limiting amplifier 107, a second electrical-signal generator 108, a second amplitude-limiting amplifier 109, a first direct-current power source 110, and a second direct-current power source 111.
  • FIG. 1 shows a structural relationship between all components of the PAM4 signal generation apparatus 100 in this embodiment of the present invention.
  • An input port of the DFB 101 is connected to the first direct-current power source 110, and the DFB 101 is connected to both the first EA modulator 102 and the SOA 104 by using two output ports.
  • the first EA modulator 102 is connected to both the first amplitude-limiting amplifier 107 and the DFB 101 by using two input ports, and an output port of the first EA modulator 102 is connected to the PSR 105.
  • the SOA 104 is connected to both the DFB 101 and the second direct-current power source 111 by using two input ports, and an output port of the SOA 104 is connected to the second EA modulator 103.
  • the second EA modulator 103 is connected to both the second amplitude-limiting amplifier 109 and the SOA 104 by using two input ports, and an output port of the second EA modulator 103 is connected to the PSR 105.
  • the PSR 105 is connected to both the first EA modulator 102 and the second EA modulator 103 by using two input ports.
  • the first electrical-signal generator 106 is connected to the first amplitude-limiting amplifier 107, and the second electrical-signal generator 108 is connected to the second amplitude-limiting amplifier 109.
  • the PAM4 signal generation apparatus includes the DFB, the two EA modulators, the SOA, the PSR, the direct-current power sources, the two electrical-signal generators, and the two amplitude-limiting amplifiers.
  • the two EA modulators may generate two NRZ optical signals with different amplitudes by using the DFB and the SOA, and the PSR may multiplex the two NRZ optical signals with different amplitudes, to generate a PAM4 signal.
  • the following describes a process of generating the PAM4 signal in the PAM4 signal generation apparatus shown in FIG. 1 . Functions of all components of the PAM4 signal generation apparatus are as follows:
  • the DFB is configured to: receive a first direct-current bias signal input by the first direct-current power source, generate a first optical signal and a second optical signal according to the first direct-current bias signal separately, transmit the first optical signal to the first EA modulator, and transmit the second optical signal to the SOA, where the first optical signal and the second optical signal have a same wavelength.
  • the first EA modulator is configured to: receive a first NRZ electrical signal input by the first electrical-signal generator by using the first amplitude-limiting amplifier, receive the first optical signal input by the DFB, obtain a first NRZ optical signal by means of modulation according to the first NRZ electrical signal and the first optical signal, and transmit the first NRZ optical signal to the PSR.
  • the SOA is configured to: receive a second direct-current bias signal input by the second direct-current power source, receive the second optical signal input by the DFB, adjust an optical power of the second optical signal according to the second direct-current bias signal to obtain a second optical signal that is after optical power amplification, and transmit, to the second EA modulator, the second optical signal that is after optical power amplification.
  • the second EA modulator is configured to: receive a second NRZ electrical signal input by the second electrical-signal generator by using the second amplitude-limiting amplifier, receive the second optical signal that is after optical power amplification and that is input by the SOA, obtain a second NRZ optical signal by means of modulation according to the second NRZ electrical signal and the second optical signal that is after optical power amplification, and transmit the second NRZ optical signal to the PSR.
  • the PSR is configured to: receive the first NRZ optical signal input by the first EA modulator, receive the second NRZ optical signal input by the second EA modulator, multiplex the first NRZ optical signal and the second NRZ optical signal, and output the PAM4 signal.
  • the DFB may generate two optical signals.
  • the optical signals are original optical signals before being modulated by the EAs.
  • the DFB is connected to the first direct-current power source.
  • the first direct-current power source generates the first direct-current bias signal (that is, the first BIAS), and inputs the first direct-current bias signal to the DFB.
  • the DFB Triggered by the first direct-current bias signal, the DFB generates the two optical signals separately.
  • the two output ports of the DFB are connected to the first EA modulator and the SOA respectively, and the two optical signals generated by the DFB are sent to the first EA modulator and the SOA respectively.
  • the first EA modulator is connected to the first amplitude-limiting amplifier
  • the first amplitude-limiting amplifier is connected to the first electrical-signal generator
  • the first electrical-signal generator generates the first NRZ electrical signal
  • the first NRZ electrical signal is input to the first EA modulator after undergoing amplitude-limiting amplification performed by the first amplitude-limiting amplifier.
  • the first amplitude-limiting amplifier is specifically configured to: receive an input signal that presents a binary data stream, to perform amplification for the input signal with a high gain to a saturated state, and output a substantive second-order output signal that presents a binary data stream.
  • the first amplitude-limiting amplifier has a high-gain function, so that the first amplitude-limiting amplifier can amplify an input signal to the saturated state. In addition, the first amplitude-limiting amplifier has an enough speed to keep pace with a quickly changed input signal.
  • the first EA modulator obtains the first NRZ optical signal by means of modulation according to the first NRZ electrical signal and the first optical signal.
  • the first EA modulator is an optical signal modulation device produced by using an exciton absorption effect in a semiconductor, and is characterized by a high response speed and low power consumption.
  • the first EA modulator may be configured to perform signal modulation and coding in high-speed fiber-optic communication. After generating the first NRZ optical signal, the first EA modulator transmits the first NRZ optical signal to the PSR.
  • the SOA is connected to the second direct-current power source and the DFB, and the second direct-current power source generates the second direct-current bias signal (that is, the second BIAS), and inputs the second direct-current bias signal to the SOA.
  • a function of the SOA is to perform amplification for an optical signal.
  • An amplification circuit of the SOA can work only based on a direct-current bias.
  • the second direct-current power source may provide the second direct-current bias signal for the SOA.
  • the SOA is used to perform amplification for the to-be-transmitted signal. In this way, amplification can be directly performed for an optical signal without optical-to-electrical conversion or electrical-to-optical conversion.
  • the SOA amplifies the optical power of the second optical signal input by the DFB, so as to obtain the second optical signal whose optical power is twice that of the first optical signal.
  • the two EA modulators can generate two NRZ optical signals with different amplitudes.
  • the second EA modulator is connected to the second amplitude-limiting amplifier
  • the second amplitude-limiting amplifier is connected to the second electrical-signal generator
  • the second electrical-signal generator generates the second NRZ electrical signal
  • the second NRZ electrical signal is input to the second EA modulator after undergoing amplitude-limiting amplification performed by the second amplitude-limiting amplifier.
  • the second amplitude-limiting amplifier is specifically configured to: receive an input signal that presents a binary data stream, to perform amplification for the input signal with a high gain to a saturated state, and output a substantive second-order output signal that presents a binary data stream.
  • the second amplitude-limiting amplifier has a high-gain function, so that the second amplitude-limiting amplifier can amplify an input signal to the saturated state. In addition, the second amplitude-limiting amplifier has an enough speed to keep pace with a quickly changed input signal.
  • the second EA modulator obtains the second NRZ optical signal by means of modulation according to the second NRZ electrical signal and the second optical signal.
  • the second EA modulator is an optical signal modulation device produced by using an exciton absorption effect in a semiconductor, and is characterized by a high response speed and low power consumption.
  • the second EA modulator may be configured to perform signal modulation and coding in high-speed fiber-optic communication. After generating the second NRZ optical signal, the second EA modulator transmits the second NRZ optical signal to the PSR.
  • the PSR has a multiplexing function.
  • the PSR receives the first NRZ optical signal input by the first EA modulator and receives the second NRZ optical signal input by the second EA modulator.
  • the PSR multiplexes the first NRZ optical signal and the second NRZ optical signal to generate the PAM4 signal, and then the PSR outputs the generated PAM4 signal.
  • the first electrical-signal generator is configured to pre-compensate the first NRZ electrical signal according to a relative delay that is between the first NRZ electrical signal and the second NRZ electrical signal and that is on a transmission optical path.
  • a transmission time delay occurs, on a transmission optical path, on the two NRZ optical signals generated by the first EA modulator and the second EA modulator, that is, a skew is generated between the two NRZ optical signals, for example, there is a delay of 10 picoseconds that is between the two NRZ optical signals and that is on the transmission optical path, the skew between the two NRZ optical signals may be pre-compensated on the NRZ electrical signals. Therefore, an optical path compensation unit is not required on the optical path; in this case, a device design is further simplified, optical path compensation does not need to be performed dedicatedly, and signal modulation is more flexible.
  • the first electrical-signal generator may perform pre-compensation when generating the first NRZ electrical signal, so as to eliminate the relative delay that is between the two NRZ electrical signals and that is on the transmission optical path, that is, the skew between the two NRZ electrical signals may be eliminated.
  • the first electrical-signal generator performs pre-compensation, so that the first electrical-signal generator can eliminate the relative delay between the first NRZ electrical signal and the second NRZ electrical signal when obtaining the first NRZ electrical signal by means of modulation.
  • the second electrical-signal generator is configured to pre-compensate the second NRZ electrical signal according to a relative delay that is between the second NRZ electrical signal and the first NRZ electrical signal and that is on a transmission optical path.
  • a transmission time delay occurs, on a transmission optical path, on the two NRZ optical signals generated by the first EA modulator and the second EA modulator, that is, a skew is generated between the two NRZ optical signals, for example, there is a delay of 10 picoseconds that is between the two NRZ optical signals and that is on the transmission optical path, the skew between the two NRZ optical signals may be pre-compensated on the NRZ electrical signals. Therefore, an optical path compensation unit is not required on the optical path; in this case, a device design is further simplified, optical path compensation does not need to be performed dedicatedly, and signal modulation is more flexible.
  • the second electrical-signal generator may perform pre-compensation when generating the second NRZ electrical signal, so as to eliminate the relative delay that is between the two NRZ electrical signals and that is on the transmission optical path, that is, the skew between the two NRZ electrical signals may be eliminated.
  • the second electrical-signal generator performs pre-compensation, so that the second electrical-signal generator can eliminate the relative delay between the second NRZ electrical signal and the first NRZ electrical signal when obtaining the second NRZ electrical signal by means of modulation.
  • a current value of the first direct-current bias signal is less than a current value of the second direct-current bias signal.
  • the first direct-current power source is connected to the DFB, and the second direct-current power source may be connected to the SOA.
  • the first direct-current power source may generate the first direct-current bias signal, and the second direct-current power source generates the second direct-current bias signal.
  • the current value of the first direct-current bias signal generated by the first direct-current power source may range from 70 milliamperes to 100 milliamperes
  • the current value of the second direct-current bias signal generated by the second direct-current power source may range from 70 milliamperes to 100 milliamperes.
  • direct-current bias signals required by the DFB and the SOA are different.
  • the first direct-current bias signal is set as required by the DFB during optical signal generation
  • the second direct-current bias signal is set as required by the SOA.
  • an optical power of the first optical signal is equal to the optical power of the second optical signal.
  • the DFB may generate two optical signals, which are the first optical signal and the second optical signal respectively. Because lasers are output by a same DFB, the two optical signals have an exactly same wavelength, and the optical powers of the two optical signals may also be exactly the same. It should be noted that because the SOA is further connected to the DFB, and the SOA may amplify the optical power of the second optical signal, the optical power of the first optical signal and the optical power of the second optical signal may be unequal. This specifically depends on a manner of generating an optical signal by the DFS in a different application scenario.
  • the SOA is specifically configured to amplify the optical power of the second optical signal according to an optical power of the first optical signal to obtain the second optical signal that is after optical power amplification, where an optical power of the second optical signal that is after optical power amplification is twice the optical power of the first optical signal.
  • an optical power of the second NRZ optical signal generated by the second EA modulator is twice an optical power of the first NRZ optical signal generated by the first EA modulator.
  • the SOA amplifies the optical power of the second optical signal doubly, to obtain the second optical signal that is after optical power amplification.
  • the optical power of the second optical signal that is after optical power amplification is twice the optical power of the first optical signal. If the optical power of the first optical signal is unequal to the optical power of the second optical signal, the SOA amplifies the optical power of the second optical signal according to the optical power of the first optical signal to obtain the second optical signal that is after optical power amplification.
  • the optical power of the second optical signal that is after optical power amplification is twice the optical power of the first optical signal.
  • the first optical signal and the second optical signal are modulated by the first EA modulator and the second EA modulator respectively, and the optical power of the second NRZ optical signal is twice the optical power of the first NRZ optical signal, so as to meet a signal amplitude requirement of the PAM4 signal.
  • an input port of the DFB is connected to the first direct-current power source
  • an input port of the SOA is connected to the second direct-current power source.
  • the first direct-current bias signal and the second direct-current bias signal may be generated by different direct-current power sources.
  • the first direct-current power source generates the first direct-current bias signal
  • the second direct-current power source generates the second direct-current bias signal.
  • the DFB is specifically configured to: adjust a reflection coefficient of a first end surface, adjust a reflection coefficient of a second end surface, generate the first optical signal by using the first end surface, and generate the second optical signal by using the second end surface.
  • the DFB needs to adjust both the reflection coefficient of the first end surface and the reflection coefficient of the second end surface when generating the two optical signals.
  • the reflection coefficient of the two end surfaces of the DFB are adjusted to make output optical powers of the two output ports be the same.
  • the first electrical-signal generator is specifically a first digital signal processor (DSP), and the second electrical-signal generator is specifically a second DSP.
  • DSPs may be used to generate the NRZ electrical signals.
  • a DSP may be selected according to an actual scenario to generate an NRZ electrical signal.
  • the DFB is specifically configured to: transmit the first optical signal to the first EA modulator by using a first passive optical waveguide, and transmit the second optical signal to the SOA by using a second passive optical waveguide.
  • the DFS is configured to: generate two optical signals from a same source, use the passive optical waveguides to separate the two optical signals, guide the two optical signals into the first EA modulator and the SOA respectively, and output the modulated optical signals from the two ports of the DFB respectively.
  • the PAM4 signal generation apparatus includes the DFB, the two EA modulators, the SOA, the PSR, the direct-current power sources, the two electrical-signal generators, and the two amplitude-limiting amplifiers.
  • the two electrical-signal generators and the two amplitude-limiting amplifiers are used to generate the two NRZ electrical signals
  • the DFB outputs the two optical signals
  • the SOA amplifies an optical power of one of the optical signals
  • the two EA modulators may generate the two NRZ optical signals by separately using the NRZ electrical signals and the optical signals including "a large signal and a small signal”
  • the two NRZ optical signals are multiplexed by the PSR to generate a PAM4 electrical signal.
  • a linearity requirement is greatly lowered.
  • the DFB, the two EA modulators, and the SOA are used, implementing a high-linearity PAM4 code.
  • PAM4 modulation is performed in an optical domain, and this prevents a PAM4 signal from being generated on an electrical signal.
  • an amplitude-limiting device may continue to be used, with no need to use an expensive linear electrical device, to modulate the electrical signal to the optical domain in a distortionless way. Therefore, a high-quality PAM4 signal can be generated in this embodiment of the present invention.
  • a single-ended EML or a single-ended DML device is used, an NRZ signal may be obtained by means of modulation, an optical signal cannot be directly modulated into a PAM4 signal within the device, the single-ended EML cannot generate a PAM4 signal of relatively high quality due to a linearity limitation, and the single-ended DML device cannot generate a PAM4 signal of relatively high quality either due to impact of characteristics of high and low temperatures and a noise characteristic that are of the single-ended DML device.
  • FIG. 2 is a schematic flowchart of generating a PAM4 signal in a PAM4 signal generation apparatus.
  • the PAM4 signal generation apparatus provided in this embodiment of the present invention includes a DFB, two EA modulators (for example, an EA 1 and an EA 2), an SOA, a PSR, two direct-current power sources (for example, a direct-current power source 1 and a direct-current power source 2), two electrical-signal generators (for example, an electrical-signal generator 1 and an electrical-signal generator 2), and two amplitude-limiting amplifiers (for example, an amplitude-limiting amplifier 1 and an amplitude-limiting amplifier 2).
  • a PAM4 signal is generated by using the foregoing integrated device.
  • a process of generating a PAM4 optical signal is as follows:
  • the direct-current power source 1 generates a direct-current bias signal 1
  • the direct-current bias signal 1 is input to the DFB
  • the direct-current power source 2 generates a direct-current bias signal 2
  • the direct-current bias signal 2 is input the SOA. Reflection coefficients of two ports of the DFB are adjusted, so that output optical powers of continuous-wave light on the two output ports are the same, and an optical signal P1 and an optical signal P2 are generated.
  • the optical signal P2 is driven by using an NRZ1 electrical signal, and a first NRZ optical signal (that is, the NRZ1 optical signal) is generated according to the optical signal P2 and is recorded as NRZ1_out.
  • a semiconductor optical amplifier is on the right of the DFB has a main function of adjusting an output amplitude.
  • optimization is performed by using the direct-current bias signal 2, an optical signal P3 is generated after amplification is performed for the optical signal PI, and the optical signal P3 is injected into a second electro-absorption modulator (that is, the EA 2) of the integrated device, and then is driven by using an NRZ electrical signal to generate a second NRZ optical signal that is recorded as NRZ2_out.
  • the two NRZ optical signals may be combined in a PSR to form a complete PAM4 signal.
  • a skew between the two NRZ optical signals may be pre-compensated on the NRZ electrical signals. Therefore, an optical path compensation unit is not required on an optical path; in this case, a device design is further simplified, optical path compensation does not need to be performed dedicatedly, and signal modulation is more flexible.
  • the PAM4 signal obtained based on the foregoing method is not limited by device linearity.
  • the two electro-absorption modulators both perform NRZ modulation, and work in curve modulation saturation and cut-off areas, the solution proposed in this embodiment of the present invention imposes no special requirement on the device linearity provided that a low-cost amplitude limiting device is used. This is conducive to increasing an entire yield of the device.
  • the direct-current optical signal P2 is output from a left end of the DFB, passes through the electro-absorption modulator EA1, and then is modulated into the NRZ optical signal. It should be noted that because the NRZ optical signal is modulated by the EA1, a corresponding electronic driver is an amplitude-limiting amplifier.
  • the direct-current optical signal P1 is output from a right end of the DFB, and passes through a gain amplifying area of the SOA before being modulated.
  • the direct-current optical signal P3 2 x P1
  • an NRZ electrical signal is loaded after the direct-current optical signal P3 passes through the EA 2.
  • the two NRZ optical signals form a PAM4 signal after being multiplexed by the PSR. As shown in Table 1, four levels of the PAM4 signal are obtained by four different combinations of the two NRZ optical signals.
  • An embodiment of the present invention provides a new PAM4 signal generation apparatus that uses a PAM4 signal generation method based on two NRZ optical signals.
  • An existing single-ended EML is improved, and an electro-absorption modulator and an active gain area are added to two sides of a DFB to generate a PAM4 signal.
  • a device linearity requirement of the PAM4 signal generation apparatus provided in this embodiment of the present invention is greatly lowered, and a structure of the DFB plus double EAs plus the SOA implements a high-linearity PAM4 code.
  • the PAM4 signal generation apparatus in this embodiment of the present invention may be based on an existing InP technology, has a same package procedure as an indium phosphide (InP) laser/a semiconductor optical amplifier, does not require a new technological process, and is completely compatible with the existing technology, reducing device costs.
  • This embodiment of the present invention may be conducive to reducing device difficulty. Because PAM4 modulation is performed on direct-current optical signal, no PAM4 signal needs to be used on an electrical signal. In this way, a prior-art amplitude-limiting device can continue to be used, and no linear electrical device needs to be used.
  • connection relationships between modules indicate that the modules have communication connections with each other, and may be specifically implemented as one or more communications buses or signal cables or optical fibers.
  • the present invention may be implemented by necessary universal hardware or by dedicated hardware including a dedicated integrated circuit, a dedicated CPU, a dedicated memory, a dedicated component, and the like.
  • a specific hardware structure used to implement a same function may also be diversified, for example, an analog circuit, a digital circuit, or a dedicated circuit.

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Claims (10)

  1. Appareil de génération de signaux à modulation d'impulsions en amplitude sur quatre niveaux (PAM4) (100), l'appareil de génération de signaux PAM4 (100) comprenant un laser à rétroaction répartie (DFB) (101), un premier modulateur électroabsorbant (EA) (102), un second modulateur EA (103), un amplificateur optique à semiconducteur (SOA) (104), un rotateur de séparation de faisceau et de polarisation (PSR) (105), un premier générateur de signaux électriques (106), un premier amplificateur de limitation d'amplitude (107), un second générateur de signaux électriques (108), un second amplificateur de limitation d'amplitude (109), une première source électrique en courant continu (110) et une seconde source électrique en courant continu (111) ;
    un port d'entrée du DFB (101) étant connecté à la première source électrique en courant continu (110), et le DFB (101) étant connecté au premier modulateur EA (102) et au SOA (104) au moyen de deux ports de sortie ;
    le premier modulateur EA (102) étant connecté au premier amplificateur de limitation d'amplitude (107) et au DFB (101) au moyen de deux ports d'entrée, et un port de sortie du premier modulateur EA (102) étant connecté au PSR (105) ;
    le SOA (104) étant connecté au DFB (101) et à la seconde source électrique en courant continu (111) au moyen de deux ports d'entrée, et un port de sortie du SOA (104) étant connecté au second modulateur EA (103) ;
    le second modulateur EA (103) étant connecté au second amplificateur de limitation d'amplitude (109) et au SOA (104) au moyen de deux ports d'entrée, et un port de sortie du second modulateur EA (103) étant connecté au PSR (105) ;
    le PSR (105) étant connecté au premier modulateur EA (102) et au second modulateur EA (103) au moyen de deux ports d'entrée ;
    le premier générateur de signaux électriques (106) étant connecté au premier amplificateur de limitation d'amplitude (107), et le second générateur de signaux électriques (108) étant connecté au second amplificateur de limitation d'amplitude (109) ;
    le DFB (101) étant configuré pour : recevoir un premier signal de polarisation en courant continu entré par la première source électrique en courant continu (110), générer séparément un premier signal optique et un second signal optique selon le premier signal de polarisation en courant continu, transmettre le premier signal optique au premier modulateur EA (102) et transmettre le second signal optique au SOA (104), le premier signal optique et le second signal optique ayant une même longueur d'onde ; le premier modulateur EA (102) étant configuré pour : recevoir un premier signal électrique sans retour à zéro (NRZ) entré par le premier générateur de signaux électriques (106) au moyen du premier amplificateur de limitation d'amplitude (107), recevoir le premier signal optique entré par le DFB (101), obtenir un premier signal optique NRZ au moyen d'une modulation selon le premier signal électrique NRZ et le premier signal optique, et transmettre le premier signal optique NRZ au PSR (105) ; le SOA (104) étant configuré pour: recevoir un second signal de polarisation en courant continu entré par la seconde source électrique en courant continu (111), recevoir le second signal optique entré par le DFB (101), régler une puissance optique du second signal optique selon le second signal de polarisation en courant continu pour obtenir un second signal optique obtenu après amplification de puissance optique, et transmettre, au second modulateur EA (103), le second signal optique obtenu après amplification de puissance optique ;
    le second modulateur EA (103) étant configuré pour: recevoir un second signal électrique NRZ entré par le second générateur de signaux électriques (108) au moyen du second amplificateur de limitation d'amplitude (109), recevoir le second signal optique obtenu après amplification de puissance optique et entré par le SOA (104), obtenir un second signal optique NRZ au moyen d'une modulation selon le second signal électrique NRZ et le second signal optique obtenu après amplification de puissance optique, et transmettre le second signal optique NRZ au PSR (105) ; et
    le PSR (105) étant configuré pour : recevoir le premier signal optique NRZ entré par le premier modulateur EA (102), recevoir le second signal optique NRZ entré par le second modulateur EA (103), multiplexer le premier signal optique NRZ et le second signal optique NRZ, et produire un signal PAM4.
  2. Appareil de génération de signaux PAM4 (100) selon la revendication 1, dans lequel le premier générateur de signaux électriques (106) est configuré pour précompenser le premier signal électrique NRZ selon un délai relatif qui est entre le premier signal électrique NRZ et le second signal électrique NRZ et qui est sur une voie optique de transmission.
  3. Appareil de génération de signaux PAM4 (100) selon la revendication 1, dans lequel le second générateur de signaux électriques (108) est configuré pour précompenser le second signal électrique NRZ selon un délai relatif qui est entre le second signal électrique NRZ et le premier signal électrique NRZ et qui est sur une voie optique de transmission.
  4. Appareil de génération de signaux PAM4 (100) selon la revendication 1, dans lequel une valeur de courant du premier signal de polarisation en courant continu est inférieure à une valeur de courant du second signal de polarisation en courant continu.
  5. Appareil de génération de signaux PAM4 (100) selon la revendication 1, dans lequel une puissance optique du premier signal optique est égale à la puissance optique du second signal optique.
  6. Appareil de génération de signaux PAM4 (100) selon la revendication 1, dans lequel le SOA (104) est spécifiquement configuré pour amplifier la puissance optique du second signal optique selon une puissance optique du premier signal optique pour obtenir le second signal optique obtenu après amplification de puissance optique, une puissance optique du second signal optique obtenu après amplification de puissance optique étant égale à deux fois la puissance optique du premier signal optique.
  7. Appareil de génération de signaux PAM4 (100) selon la revendication 6, dans lequel une puissance optique du second signal optique NRZ généré par le second modulateur EA (103) est égale à deux fois une puissance optique du premier signal optique NRZ généré par le premier modulateur EA (102).
  8. Appareil de génération de signaux PAM4 (100) selon l'une quelconque des revendications 1 à 7, dans lequel le DFB (101) est spécifiquement configuré pour : régler un coefficient de réflexion d'une première surface extrême, régler un coefficient de réflexion d'une seconde surface extrême, générer le premier signal optique au moyen de la première surface extrême et générer le second signal optique au moyen de la seconde surface extrême.
  9. Appareil de génération de signaux PAM4 (100) selon l'une quelconque des revendications 1 à 7, dans lequel le premier générateur de signaux électriques (106) est spécifiquement un premier dispositif de traitement de signaux numériques (DSP) ; et le second générateur de signaux électriques (108) est spécifiquement un second DSP.
  10. Appareil de génération de signaux PAM4 (100) selon l'une quelconque des revendications 1 à 7, dans lequel le DFB (101) est spécifiquement configuré pour : transmettre le premier signal optique au premier modulateur EA (102) au moyen d'un premier guide d'ondes optiques passif et transmettre le second signal optique au SOA (104) au moyen d'un second guide d'ondes optiques passif.
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